1. Field of the Invention
This invention relates in general to friction clutches and in particular to predampers for clutch driven disks.
2. Description of the Related Art
Clutches are well known devices used to selectively connect a source of rotational power to a driven mechanism. For instance, in a vehicle drive-train system, a clutch is used to drivingly connect an engine to a transmission. When the engine is drivingly connected with the transmission by the clutch, vibrations are transmitted through the clutch and into the transmission and other drive-train components, producing undesirable operating conditions, such as gear rattle.
Clutches generally include a clutch hub engaged for rotation with a transmission input shaft and a clutch disk selectively engaged for rotation with the engine flywheel. To reduce the transmission of vibrations, clutches typically employ a plurality of compression damping springs between the clutch hub and the clutch disc. These springs are typically disposed in spring pockets circumferentially located around the clutch hub. Compression of the damping springs is limited by stops disposed between the hub and the clutch disk, limiting relative rotation therebetween. The damping springs provide some degree of isolation between the engine and transmission to reduce the transmission of vibration due to engine firing pulses and other engine speed fluctuations. However, vibrations can still be transmitted through the damping springs to produce gear rattle.
One solution to further reducing the transmission of vibrations has been to split the hub into an inner hub directly connected to the transmission input shaft and an outer hub connected to the clutch disc through the damping springs. The inner hub and outer hub are configured to provide a predetermined amount of rotative lash between the two parts. A predamper is placed between the inner hub and the outer hub. The predamper has springs of particular rates and preload characteristics selected to further damp out vibrations that can induce gear rattle.
One known predamper configuration includes driving and driven elements; wherein the driven element is rotatably fixed to the inner hub and the driving element is rotatably fixed to the outer hub with a plurality of compression predamper springs disposed therebetween. The predamper springs are generally much smaller than, and of a much lower spring rate than, the damping springs disposed between the outer hub and the clutch disc and typically require end caps that facilitate the retention of predamper springs within the predamper. While this design has proven functionally successful, the additional components undesirably increase the axial length of the clutch package and inhibit the ability to incorporate a hysteresis component into the predamper for further torsional damping.